Generally, acrylonitrile-butadiene-styrene (ABS) resins can have superior impact resistance and processability, high mechanical strength and heat distortion temperature, and attractive appearance. Due to these advantages, ABS resins are widely used in various applications, for example, automobiles, electrical/electronic devices, office machines, household electric appliances, toys, and stationery.
However, butadiene rubber components used in ABS resins contain chemically labile double bonds and thus tend to age when exposed to sunlight or UV light. This can limit the use of ABS resins in outdoor products, including electrical/electronic components, materials for agricultural tools, road signs, building finishing materials, door panels, window frames, leisure goods, household articles, sporting goods, and automotive goods.
Many attempts have been made to improve the weather resistance of ABS resins. For example, the addition of weather stabilizers is used. However, this approach offers unsatisfactory results.
Also, considerable research efforts have concentrated on acrylate-styrene-acrylonitrile (ASA) resins using chemically stable acrylic rubbers in place of butadiene rubbers.
Some resin compounds are reinforced with acrylic rubbers to obtain improved impact strength. However, final products using the impact reinforced resin compounds can undergo significant loss of heat resistance due to inherent characteristics of the rubbers. Thus it can be difficult to use these resins in applications where high heat resistance is required. Accordingly, there is research aimed at improving the heat resistance of final products by mixing and kneading such acrylic rubber reinforced resins with resins having relatively good heat resistance.
With the recent steadily growing interest in resins that are free from a feeling of cold plastics and give a sense of warmness, there has been an increasing need for resins that have soft low-gloss surfaces and can be produced without coating. Particularly, stringent regulations for environmental protection have gradually extended the applications of low-gloss resins that can be directly molded while eliminating the need for coating.
Methods for producing low-gloss, weather resistant resins are broadly classified into three groups. The first group of methods is based on the use of inorganic fillers, acrylic resins or cross-linked styrene resins as matt additives or matting agents. The first group of methods is most widely used. The second group of methods is associated with the removal of gloss during post-processing. Such methods include, for example, methods for obtaining low-gloss effects by injection molding using etching molds or coating. The third group of methods is associated with the formation of micro-scale rough surfaces by controlling the size of particles dispersed in matrices. The surfaces scatter incident light, resulting in low gloss.
The first group of methods based on the use of matt additives or matting agents to achieve low-gloss effects is convenient in various aspects but has a limitation in increasing the quality of final products because the uniformity of gloss is determined by the dispersed state of the additives. The specific gravity of the additives is generally high, which may also lead to an increase in the specific gravity of final products.
The second group of methods using injection molding through etching molds or coating may incur considerable production costs due to the introduction of additional processing and may cause pollution, which is disadvantageous from an environmental viewpoint.
According to an approach to achieve low gloss characteristics of common ASA products, small dispersed phases aggregate into a larger volume. However, this approach necessitates an additional process for re-aggregation of particles after polymerization causing dispersion and has basic technical problems, for example, re-dispersion of the aggregated phases during mixing and kneading for the production of products.
U.S. Pat. No. 6,696,165 discloses a method for lowering the gloss of an ASA resin by the addition of about 0.1 to about 20 parts by weight of a crystalline polymer, typified by a polyalkyl terephthalate, and U.S. Pat. No. 6,395,828 discloses a method for lowering the gloss of an ASA resin by the addition of 0.5 to 15 parts by weight of a reaction product of an epoxy compound and an amine compound.
Methods for lowering the gloss of resins by the use of spherical graft copolymers as matting agents are disclosed, for example, in U.S. Pat. Nos. 5,475,053 and 4,652,614. Methods for lowering the gloss of resins by the use of various copolymers as additives are disclosed, for example, in U.S. Pat. Nos. 4,169,869, 4,460,742 and 5,580,924, and Korean Patent Publication No. 2008-0036790.
Other methods are disclosed, for example, in U.S. Pat. Nos. 4,668,737 and 5,237,004. In these methods, core/shell structured rubber particles having a large particle diameter of 0.05 to 20 μm or 2 to 15 μm are used to lower the gloss of resins.
However, the use of such additives may lead to an increase in production cost and may cause problems of peeling, poor physical properties and partially increased gloss. The use of large rubber particles disadvantageously causes a drastic reduction in impact strength despite the advantage of low gloss.
There is thus a need to develop a low-gloss thermoplastic resin that has good resistance to heat and weather without deterioration of other physical properties, such as impact strength and flowability.